CN115225246A - Phase modulation bidirectional time synchronization device, method and system - Google Patents
Phase modulation bidirectional time synchronization device, method and system Download PDFInfo
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Abstract
The invention discloses a phase modulation bidirectional time synchronization device, method and system, belonging to the time synchronization field; at the near end, the received far end signal and the light of the laser are mixed directly by the beam splitter, then input into the balanced homodyne detection and demodulation and converted into an electric signal, a time signal is obtained by the time measuring module, and the time difference T between the far end time signal and the near end sending time signal is obtained by comparison A And transmitted to the remote end. At the far end, the received near-end second pulse signal and the light of the far-end laser are mixed by a beam splitter, then input into a balanced homodyne for detection and demodulation and converted into an electric signal, a time signal is obtained by a time measuring module, and the time difference T between the received near-end time signal and the far-end sending time signal is obtained by comparison B And time difference T from near-end transmission A And calculating the time delay difference of the link, thereby performing feedback adjustment on a clock source at a far end and compensating the generated time delay difference. The invention eliminates the bias drift problem and asymmetry.
Description
Technical Field
The invention belongs to the field of time synchronization, and particularly relates to a phase modulation bidirectional time synchronization device, method and system.
Background
The time synchronization among different positions plays an important role in many applications, and basic research fields such as comparison and synchronization among atomic clocks, synchronization of long-base-line coherent radio telescopes, particle accelerators, or global positioning systems, precise guidance of rockets and missiles, phased radar array coordination control, burst confidential communication and the like relate to the application of the national strategic level and are not separated from high-precision time synchronization, so that the high-precision and high-stability time synchronization technology plays an increasingly prominent role in scientific research and national life.
Compared with the traditional two-way satellite time and frequency transmission, the optical fiber link has the advantages of large bandwidth, low loss, small temperature coefficient, low manufacturing cost, high stability, long relay distance and strong anti-interference capability, and is considered as a promising substitute medium for high-stability and long-distance time transmission. However, the time delay of the fiber optic link is drifting, mainly caused by mechanical disturbances and temperature variations. One of the classical approaches to overcome this problem is to arrange a bidirectional transmission of a time signal in both participating stations, known as a bidirectional time synchronization system. Another approach is to redirect signals arriving at the remote site back to the local site, also known as a loopback time synchronization system. Both of these solutions are indispensable for comparing the local signal with the signal received by each station. According to the comparison result of the far and near sites, the dynamic compensation and calibration can be carried out on the transmission delay fluctuation so as to improve the stability of the time transmission system.
At present, the research on the optical fiber time synchronization system at home and abroad has been greatly developed. Research on optical fiber time frequency signal transmission in developed countries such as Europe and America has made breakthrough progress. In 2010, a Czech education and scientific research network center realizes time synchronization transmission on an on-site optical fiber link of 744km by using a wavelength division multiplexing two-way time comparison method, and the stability is superior to 100ps @1s and the uncertainty is 112ps. In 2016, the VSL of the Dutch national measurement institute adopts a bidirectional optical amplifier structure and a White Rabbit system, realizes time synchronization transmission on an 274 km optical fiber link, and has uncertainty superior to 8.2ns. In 2019, the university of poland clakov AGH technologies proposed a method of correcting phase delay by changing the length or temperature of the optical fiber dispersion compensation module, which achieved a time transmission stability better than 20ps over a 1550km field optical fiber link. In China, in 2017, the Qinghua university realizes high-precision multi-channel optical fiber time signal synchronous transmission on an optical fiber link of 25km, the stability is superior to 3ps @1s, and the uncertainty is about 100ps. 2019. In the year, shanghai traffic university proposes a method for time transmission through an optical monitoring channel in a commercial wavelength division multiplexing system, and obtains more than 15ps @1s and 2ps @10 on a laboratory optical fiber link of 100 km 4 s time transfer stability. In 2020, the time signal and the microwave signal are simultaneously loaded onto the laser with the same wavelength by the Shanghai optical machine, and the high-precision time signal transmission is realized on a 110km laboratory optical fiber link, wherein the time transmission stability is 169s and 0.91ps @10 4 s。
A conventional two-way time synchronization system is generally shown in fig. 1, in which a near end and a far end simultaneously transmit their time information to an opposite end and simultaneously receive the time information transmitted from the opposite end. Time signal t sent by near-end clock A One path is used as a counting starting signal of a local time interval counter, and the other path is used as an optical pulse sending module and uses lambda 1 The wavelength is sent out, the wavelength division multiplexing enters an optical fiber link, optical signals at the far end are separated out through the wavelength division multiplexing, the optical signals are converted into electric signals through an optical pulse receiving module, and the second pulse recovered at the far end serves as a stop signal of a far end time interval counter. Similarly, the time signal t from the remote clock B One path is used as a counting starting signal of a far-end time interval counter, and the other path is used as an optical pulse sending module with lambda 2 The wavelengths are transmitted out by wavelength division multiplexingAnd the optical signals enter an optical fiber link, the optical signals are separated out through wavelength division multiplexing at the near end, the optical signals are converted into electric signals through an optical pulse receiving module, and the second pulse recovered at the near end is used as a stop signal of a near end time interval counter. The clock difference between the two places is calculated by measuring the time difference between the signals transmitted by the near end and the far end. By using the clock difference data, one clock source is used as a reference, and the other clock source is adjusted through servo control, so that the time synchronization of two places is realized.
However, the above system generally adopts intensity modulation during optical signal modulation, and a corresponding dc bias point needs to be set for the intensity modulator, and different bias points may affect the operating state of the intensity modulator. Because the intensity modulator can be influenced by external interference, temperature, aging and the like during use, a set direct current bias point is easy to drift, so that the transmission function of the modulator drifts, and after the drift occurs, the rising edge of a pulse per second signal detected by a receiving end changes, so that the transmission performance of the whole system is influenced.
Disclosure of Invention
Aiming at the influence of system performance caused by bias point drift during signal modulation, the invention provides a phase modulation bidirectional time synchronization device, a method and a system, wherein the phase modulation is used for changing the phase of an optical signal, and the time delay difference of a link is calculated to perform feedback adjustment on a clock source and compensate the generated time delay difference; meanwhile, through the bidirectional time synchronization of the phase modulation, the problem that the transmission performance of a system is deteriorated due to the drift of a direct current bias point easily generated when the intensity of an optical signal is modulated in the traditional bidirectional time synchronization is solved.
The phase modulation bidirectional time synchronization device comprises a near end A and a far end B;
the near-end A consists of a near-end clock source, a near-end laser, a first phase modulator, a first phase control module, a near-end balanced homodyne detector, a near-end circulator, a first beam splitter, a second beam splitter and a near-end time measuring module.
The near-end laser is connected with the first beam splitter, the output light is divided into two paths, one path enters the first phase modulator, meanwhile, a clock signal generated by a near-end clock source is also input into the first phase modulator, and the first phase modulator outputs the modulated signal light and inputs the modulated signal light into the optical fiber link through the near-end circulator; the other path is input into a second beam splitter, and meanwhile, the near-end circulator receives a far-end signal through an optical fiber link, modulates the far-end signal through the first phase control module and inputs the far-end signal into the second beam splitter; the second beam splitter combines the two paths of signals, then the two corresponding outputs jointly enter a near-end balanced homodyne detector, a far-end time pulse signal is obtained through the detector, and the far-end time pulse signal is input into a near-end time measuring module and a near-end clock source signal to calculate a time delay difference; and meanwhile, the near-end time delay is transmitted to the far-end by using the optical fiber link.
The far-end B consists of a far-end clock source, a far-end laser, a second phase modulator, a second phase control module, a far-end balanced homodyne detector, a far-end circulator, a third beam splitter, a fourth beam splitter and a far-end time measuring module.
The far-end laser is connected with the third beam splitter, the output light is divided into two paths, one path enters the third phase modulator, a clock signal generated by a far-end clock source is also input into the third phase modulator, and the signal light modulated by the third phase modulator is input into the optical fiber link through the far-end circulator; the other path is input into a fourth beam splitter, meanwhile, a far-end circulator receives near-end signals through an optical fiber link, the near-end signals are modulated through a second phase control module and input into a fourth beam splitter, the fourth beam splitter combines the two paths of signals, the corresponding two outputs jointly enter a far-end balanced homodyne detector, near-end time pulse signals are obtained through the detector, and the near-end time pulse signals are input into a far-end time measurement module and a near-end clock source signal to calculate time delay difference; meanwhile, clock difference delta T is calculated according to the time delay difference obtained by the near end, and the clock difference delta T is compensated for the clock signal of the far-end clock source, so that the time synchronization of the near end A and the far end B is finally realized.
Further, the near-end circulator or the far-end circulator is replaced by a wavelength division multiplexer; meanwhile, the two lasers are set to have different wavelengths for distinguishing.
The phase modulation bidirectional time synchronization method comprises the following steps:
firstly, a near-end clock source generates a pulse per second, modulates the pulse per second to an optical signal through a phase, and sends the pulse per second to a far end through an optical fiber link;
secondly, the far-end circulator combines the frequency of the received optical signal through the beam splitter and the light of the far-end laser, the demodulated electrical signal is obtained through the detector, and the demodulated electrical signal is input into the far-end time measuring module to obtain the time delay difference T of the time signals generated by the far end and sent by the near end B ；
Thirdly, a far-end clock source generates a pulse per second, the pulse per second is modulated to an optical signal through a phase, and the optical signal is sent to a near end through an optical fiber link;
fourthly, the near-end circulator combines the frequency of the received optical signals through the beam splitter and the light of the near-end laser, the demodulated electrical signals are obtained through the detector, and the demodulated electrical signals are input into a near-end time measuring module to obtain the time delay difference T of the time signals generated by the near end and sent by the far end A ；
Step five, the near end compares the time difference T A Sending to the remote end;
and step six, the far end calculates the clock delays of the two ends through the two time difference values, and adjusts the clock source of the far end according to the clock delays to achieve time synchronization of the far end and the near end.
The calculation formula of the clock delay is as follows:
T AB for near-end to far-end fibre-optic transmission delay, T BA The optical fiber transmission time delay from the far end to the near end; t is t A For the transmission delay of the near end A, t B Is the transmission delay of the remote B, r A Is the reception delay of the near end A, r B Δ T is the clock offset for the receive delay of the remote B.
The phase modulation bidirectional time synchronization system comprises the following contents:
and (3) balancing two paths of output of the second beam splitter by a homodyne detector at the near end A: the P signal light of the far-end optical signal transmitted by the optical fiber link after phase modulation and the output light of the laser are subjected to coherent demodulation to obtain the modulation second pulse on the P signal, and the modulation second pulse is outputEntering a near-end time measuring module, calculating a time delay difference T with a clock signal of a near-end clock source A The delay time difference T A Transmitted to the far end through the optical fiber link.
Time delay difference T A The clock difference is the time between the sending of the pulse per second signal by the near end and the receiving of the pulse per second signal sent by the far end; the calculation formula is as follows:
T A ＝ΔT+T BA +t B +r A
Δ T is the delay difference T A And delay difference T B The clock difference between; t is BA The optical fiber transmission time delay from the far end to the near end; t is t B Is the transmission delay of the remote B, r A Is the receive delay of the near end a;
meanwhile, a second pulse signal and a clock signal generated by a near-end clock source are provided for a phase modulator, and the phase modulator performs phase modulation on light output by a near-end laser according to the received electric signal output by the near-end balanced homodyne detector, converts the light into an optical signal S, and outputs the optical signal S to a far end B through an optical fiber link.
The second pulse signal and the clock signal generated by the clock source at the far end B are provided for the phase modulator, and the phase modulator performs phase modulation on light output by the far end laser according to the received electric signal output by the far end balanced homodyne detector, so as to convert the light into an optical signal P.
The far-end balanced homodyne detector performs coherent demodulation on the received optical signal S and the output light of the far-end laser to obtain a modulation second pulse on the signal S. The obtained pulse per second signal is input into a far-end time measuring module and is compared with a clock signal of a far-end clock source to calculate a time delay difference T B 。
T B A clock difference which is the time between the sending of the pulse per second signal by the far end and the receiving of the pulse per second signal sent by the near end; the calculation formula is as follows:
T B ＝-ΔT+T AB +t A +r B
T AB for near-end to far-end fibre-optic transmission delay, t A Is the transmission delay of the near end A, r B Is the receive delay of the remote B.
According to the time delay difference T at the same time A And calculating the clock difference delta T to adjust the clock signal of the far-end clock source, thereby compensating the delta T for the far-end clock source to realize the time synchronization of the far end and the near end.
The delay difference calculation formula is as follows:
the invention has the advantages that:
1) The phase modulation bidirectional time synchronization device, the phase modulation bidirectional time synchronization method and the phase modulation bidirectional time synchronization system adopt the phase modulation to generate the signal light, and the offset drift problem which often occurs in the traditional Mach-Zehnder modulator is eliminated;
2) The phase modulation bidirectional time synchronization device, method and system overcome the problem of inconsistent physical lengths of channels during bidirectional time synchronization and are beneficial to eliminating asymmetry.
Drawings
Fig. 1 is a structural diagram of a conventional bidirectional time synchronization system in the prior art;
FIG. 2 is a block diagram of a phase modulated two-way time synchronization apparatus and system employed in the present invention;
fig. 3 is a flow chart of a phase modulation bidirectional time synchronization method employed by the present invention.
Detailed Description
The invention will be described in further detail below with reference to the drawings and examples,
the invention discloses a phase modulation bidirectional time synchronization device, method and system, which adopts bidirectional time synchronization and modulates optical signals by using phases; and modulating the pulse-per-second time signal onto an optical carrier by using a phase modulator during optical signal modulation. At the near end, the received far-end signal is directly mixed with the near-end laser through a beam splitter, the mixed signal is directly input into a balanced homodyne detection and demodulation to be converted into an electric signal, the electric signal obtains a time signal through a time measuring module, and the time difference T between the received far-end time signal and the near-end sending time signal is obtained through comparison A The time is transmitted through an optical fiber linkThe difference is transmitted to the far end. At the far end, the received near-end pulse per second signal is directly mixed with the far-end laser through a beam splitter, the mixed signal is directly input into a balanced homodyne detection and demodulation and is converted into an electric signal, the electric signal obtains a time signal through a time measuring module, and the time difference T between the received near-end time signal and the far-end sending time signal is obtained through comparison B And time difference T from near-end transmission A And calculating the time delay difference of the link, thereby performing feedback adjustment on a clock source at a far end and compensating the generated time delay difference.
The phase modulation bidirectional time synchronizer, as shown in fig. 2, includes a near end a and a far end B;
the near end A consists of a near end clock source, a near end laser, a first phase modulator, a first phase control module, a near end balanced homodyne detector, a near end circulator, a first beam splitter, a second beam splitter and a near end time measuring module.
The near-end laser is connected with the first beam splitter, the output light is divided into two paths, one path enters the first phase modulator, meanwhile, a clock signal generated by a near-end clock source is also input into the first phase modulator, and the first phase modulator outputs the modulated signal light and inputs the modulated signal light into the optical fiber link through the near-end circulator; the other path is input into a second beam splitter, and meanwhile, the near-end circulator receives a far-end optical signal P through an optical fiber link, performs coherent modulation through a first phase control module and inputs the far-end optical signal P into the second beam splitter; the second beam splitter combines the two paths of signals, then the two corresponding outputs jointly enter a near-end balanced homodyne detector, a far-end time pulse signal is obtained through the detector, and the far-end time pulse signal is input into a near-end time measuring module and a near-end clock source signal to obtain a time delay difference; and meanwhile, the near-end time delay is transmitted to the far-end by using the optical fiber link.
The second pulse signal generated by the near-end clock source and the near-end clock signal are provided for the phase modulator, and the phase modulator performs phase modulation on the output light of the near-end laser according to the received electric signal and converts the output light into an optical signal S.
The far end B consists of a far end clock source, a far end laser, a second phase modulator, a second phase control module, a far end balanced homodyne detector, a far end circulator, a third beam splitter, a fourth beam splitter and a far end time measuring module.
The far-end laser is connected with the third beam splitter, the output light is divided into two paths, one path enters the third phase modulator, a clock signal generated by a far-end clock source is also input into the third phase modulator, and the signal light modulated by the third phase modulator is input into the optical fiber link through the far-end circulator; the other path is input into a fourth beam splitter, meanwhile, a far-end circulator receives near-end signal light S through an optical fiber link, the near-end signal light S is modulated through a second phase control module and input into the fourth beam splitter, the fourth beam splitter combines the two paths of signals, the two corresponding outputs jointly enter a far-end balanced homodyne detector, a near-end time pulse signal is obtained through the detector, and the near-end time pulse signal is input into a far-end time measurement module and a near-end clock source signal to obtain a time delay difference;
the second pulse signal and the clock signal generated by the far-end clock source are provided for the far-end phase modulator, and the phase modulator performs phase modulation on the output light of the far-end laser according to the received electric signal and converts the output light into an optical signal P.
Meanwhile, clock difference delta T is calculated according to the time delay difference obtained by the near end, and the clock signal of the clock source is adjusted by compensating the clock difference delta T for the clock signal of the clock source at the far end, so that the time synchronization of the near end A and the far end B is finally realized.
Further, the near-end circulator or the far-end circulator is replaced by a wavelength division multiplexer; meanwhile, the two lasers are set to have different wavelengths to be distinguished.
The phase modulation bidirectional time synchronization method, as shown in fig. 3, includes the following steps:
aiming at the near end A, a clock source sends a pulse per second signal to a phase modulator, meanwhile, the clock source sends the pulse per second signal to a time measuring module, and the time measuring module starts timing.
And step two, the near-end laser sends the light to be modulated to the phase modulator, the phase modulator modulates the second pulse signal and the laser to be modulated into an optical signal S, and the optical signal S is sent to the optical fiber link through the circulator to reach the far end B.
And step three, receiving the optical signal S by the circulator at the far end B and sending the optical signal S to the balanced homodyne detector.
Step four, the balanced homodyne detector converts the optical signal S into an electric signal through coherent demodulation and sends the electric signal to the far-end time measurement module, the time measurement module stops timing after receiving the signal, and the time delay difference T between the time signal generated at the far end and the time signal sent at the near end is measured B 。
T B ＝-ΔT+T AB +t A +r B
And fifthly, aiming at the far end B, the clock source sends a pulse per second signal to the phase modulator, meanwhile, the clock source sends the pulse per second signal to the time measurement module, and the time measurement module starts timing.
And step six, the laser sends the light to be modulated to the far-end phase modulator, the far-end phase modulator modulates the second pulse signal and the laser to be modulated into an optical signal P, and the optical signal P is sent to the optical fiber link through the circulator to reach the near end A.
And seventhly, receiving the light signal P by the near-end circulator and sending the light signal P to the balanced homodyne detector.
Step eight, the balanced homodyne detector converts the optical signal P into an electric signal through coherent demodulation and sends the electric signal to the time measurement module, the time measurement module stops timing after receiving the signal, and the time delay difference T of the time signal generated by the near end and sent by the far end is measured A 。
T A ＝ΔT+T BA +t B +r A
Step nine, the time difference T between the time signals generated by the near end and the time signals transmitted by the far end is generated by the near end A And transmitting the data to the far end through the optical fiber link.
Step ten, the far-end time measuring module generates the time difference T of the time signal sent by the near end according to the far end B Time delay difference T between time signals generated by near end and transmitted by far end A And solving to obtain the clock error delta T as follows:
T A transmit pulse-per-second signal and receive for near endClock difference, T, of time between remotely transmitted pulse-per-second signals B The clock difference is the time between the sending of the nanosecond pulse signal by the far end and the receipt of the nanosecond pulse signal sent by the near end. T is AB For near-end to far-end fibre-optic transmission delay, T BA The optical fiber transmission time delay from the far end to the near end; t is t A For the transmission delay of the near end A, t B Is the transmission delay of the remote B, r A Is the reception delay of the near end A, r B Is the receive delay of the remote B.
Since the system uses the same optical fiber link, T, to and from AB -T BA And =0. And t is A +r B -t B -r A The term is a fixed value because the same modulation and demodulation mode is used at the far end and the near end, compensation can be set before the system runs, and the generated time difference is negligible.
The clock difference Δ T can therefore be reduced to:
and step eleven, adjusting a clock source signal according to the calculated clock difference delta T of the time measuring module, thereby achieving time synchronization of the near end and the far end.
The phase modulation bidirectional time synchronization system comprises the following contents:
for the near end a: the phase modulator modulates the second pulse signal of the clock source to the laser source to be converted into an optical signal S, and meanwhile, the time measuring module receives the second pulse of the clock source to start timing.
The circulator transmits an optical signal P transmitted by a far end B transmitted by an optical fiber link to the balanced homodyne detector, performs coherent demodulation with the output light of the laser to obtain a modulated second pulse on the P signal, inputs the modulated second pulse into the near-end time measuring module, and stops timing by the time measuring module; the time measurement module obtains the time delay difference T between the second pulse signal sent by the near end and the second pulse signal sent by the far end according to the timing result A The delay time difference T A Transmitted to the far end through the optical fiber link.
Time delay difference T A The clock difference is the time between the sending of the pulse per second signal by the near end and the receiving of the pulse per second signal sent by the far end; at the near end A, when starting, the near-end clock source sends out a pulse signal, and simultaneously enters the near-end phase modulator and the near-end time measuring module, and the near-end time measuring module starts to time after receiving the pulse; after the near end receives and demodulates the far end signal light, the demodulated pulse signal is input into the near end time measuring module to stop timing, and the obtained time period is the time delay difference from the near end to the far end signal, namely:
T A ＝ΔT+T BA +t B +r A
Δ T is the delay difference T A And delay difference T B The clock difference therebetween; t is BA The optical fiber transmission time delay from the far end to the near end; t is t B Is the transmission delay of the remote B, r A Is the receive delay of the near end a;
meanwhile, a second pulse signal and a clock signal generated by a near-end clock source are provided for a phase modulator, and the phase modulator performs phase modulation on light output by a near-end laser according to the received electric signal output by the near-end balanced homodyne detector, converts the light into an optical signal S, and outputs the optical signal S to a far end B through an optical fiber link.
For the far end B: the phase modulator modulates the pulse per second signal of the clock source to the laser source, and converts the pulse per second signal into an optical signal P, and meanwhile, the time measuring module receives the pulse per second signal of the clock source and starts timing.
The second pulse signal and the clock signal generated by the clock source at the far end B are provided for the phase modulator, and the phase modulator performs phase modulation on light output by the far end laser according to the received electric signal output by the far end balanced homodyne detector, so as to convert the light into an optical signal P.
The far-end balanced homodyne detector performs coherent demodulation on the received optical signal S and the output light of the far-end laser to obtain a modulation second pulse on the signal S. Inputting the obtained pulse per second signal into a remote time measuring module, and stopping timing by the time measuring module; the time measurement module obtains a far-end sending second pulse signal and a second pulse received from a near end according to a timing resultTime delay difference T of time between impulse signals B 。
T B A clock difference which is the time between the sending of the pulse per second signal by the far end and the receiving of the pulse per second signal sent by the near end; at the far end B, when starting, the far end clock source sends out a pulse signal, and simultaneously enters the far end phase modulator and the far end time measuring module, the far end time measuring module receives the pulse and starts timing, after the far end receives and demodulates the far end signal light, the demodulated pulse signal is input into the far end time measuring module and stops timing, the obtained period of time is the time delay difference from the far end sending signal to the near end signal receiving, namely:
T B ＝-ΔT+T AB +t A +r B
T AB for near-end to far-end fibre-optic transmission delay, t A Is the transmission delay of the near end A, r B Is the receive delay of the remote B.
According to time delay difference T at the same time A And calculating the clock difference delta T to adjust the clock signal of the far-end clock source, thereby compensating the delta T for the far-end clock source to realize the time synchronization of the far end and the near end.
The time delay difference of one end is transmitted to the other end through the optical fiber link, and under the condition of simultaneously obtaining two time delay differences, the clock difference delta T can be obtained by subtracting the two time delay differences:
wherein, T AB -T BA The delay difference generated for the fiber link. In the system, the optical fiber link is the same optical fiber, so that the delay term does not exist, and the clock error formula can be simplified as follows:
wherein t is A +r B -t B -r A Both the transmission delay and the reception delay are caused by delays inside the devices at both ends. First, in the systemThe near end and the far end are highly symmetrical, and the adopted devices and structures are the same, so the time delay influence is small. Secondly, before the system starts to operate, two ends can be directly connected, and at the moment, calibration is firstly carried out, so that t can be completely eliminated A +r B -t B -r A The influence of the terms, after the above process, the final clock error formula can be simplified as:
Claims (5)
1. phase modulation bidirectional time synchronizer, including near-end A and distal end B, characterized by:
the near end A consists of a near end clock source, a near end laser, a first phase modulator, a first phase control module, a near end balanced homodyne detector, a near end circulator, a first beam splitter, a second beam splitter and a near end time measuring module;
the near-end laser is connected with the first beam splitter, the output light is divided into two paths, one path enters the first phase modulator, meanwhile, a clock signal generated by a near-end clock source is also input into the first phase modulator, and the first phase modulator outputs the modulated signal light and inputs the modulated signal light into the optical fiber link through the near-end circulator; the other path is input into a second beam splitter, and meanwhile, the near-end circulator receives a far-end signal through an optical fiber link, modulates the far-end signal through the first phase control module and inputs the far-end signal into the second beam splitter; the second beam splitter combines the two paths of signals, then the two corresponding outputs jointly enter a near-end balanced homodyne detector, a far-end time pulse signal is obtained through the detector, and the far-end time pulse signal is input into a near-end time measuring module and a near-end clock source signal to obtain a time delay difference; meanwhile, the near-end time delay is transmitted to the far-end by using an optical fiber link;
the far-end B consists of a far-end clock source, a far-end laser, a second phase modulator, a second phase control module, a far-end balanced homodyne detector, a far-end circulator, a third beam splitter, a fourth beam splitter and a far-end time measuring module;
the far-end laser is connected with the third beam splitter, the output light is divided into two paths, one path enters the third phase modulator, a clock signal generated by a far-end clock source is also input into the third phase modulator, and the signal light modulated by the third phase modulator is input into the optical fiber link through the far-end circulator; the other path is input into a fourth beam splitter, meanwhile, a far-end circulator receives a near-end signal through an optical fiber link, the near-end signal is modulated through a second phase control module and input into a fourth beam splitter, the fourth beam splitter combines the two paths of signals, the two corresponding outputs jointly enter a far-end balanced homodyne detector, a near-end time pulse signal is obtained through the detector, and the near-end time pulse signal is input into a far-end time measuring module and a near-end clock source signal to obtain a time delay difference; meanwhile, clock difference delta T is calculated according to the time delay difference obtained by the near end, and the clock difference delta T is compensated for the clock signal of the far-end clock source, so that the time synchronization of the near end A and the far end B is finally realized.
2. The phase modulated bi-directional time synchronizer of claim 1 wherein the proximal circulator or the distal circulator is replaced with a wavelength division multiplexer, and wherein the two lasers are set at different wavelengths for discrimination.
3. The phase modulation bidirectional time synchronization method of the phase modulation bidirectional time synchronization apparatus according to claim 1, characterized by comprising the steps of:
firstly, a near-end clock source generates a pulse per second, the pulse per second is modulated onto an optical signal through a phase, and the optical signal is sent to a far end through an optical fiber link;
secondly, the far-end circulator combines the frequency of the received optical signal through the beam splitter and the light of the far-end laser, the demodulated electrical signal is obtained through the detector, and the demodulated electrical signal is input into the far-end time measuring module to obtain the time delay difference T of the time signals generated by the far end and sent by the near end B ；
Thirdly, a far-end clock source generates a pulse per second, the pulse per second is modulated to an optical signal through a phase, and the optical signal is sent to a near end through an optical fiber link;
fourthly, the near-end circulator combines the frequency of the received optical signal through the beam splitter and the light of the near-end laser, and the combined frequency is obtained through the detectorObtaining the demodulated electric signal, inputting the demodulated electric signal into a near-end time measuring module to obtain the time delay difference T of the time signals generated by the near end and sent by the far end A ；
Step five, the near end compares the time difference T A Sending to the far end;
step six, the far end calculates the clock delays of the two ends through two time difference values, and adjusts a far-end clock source according to the clock delays to achieve time synchronization of the far end and the near end;
the calculation formula of the clock delay is as follows:
T AB for near-end to far-end fibre-optic transmission delay, T BA The optical fiber transmission time delay from the far end to the near end; t is t A For the transmission delay of the near end A, t B Is the transmission delay of the remote B, r A Is the reception delay of the near end A, r B Δ T is the clock offset for the receive delay of the remote B.
4. A phase modulation bidirectional time synchronization system of a phase modulation bidirectional time synchronization apparatus according to claim 1, characterized by comprising:
and (3) balancing two paths of output of the second beam splitter by a homodyne detector at the near end A: the P signal light after the far-end light signal transmitted by the optical fiber link is subjected to phase modulation and the output light of the laser, the coherent demodulation is carried out to obtain the modulation second pulse on the P signal, the modulation second pulse is input into the near-end time measuring module, and the time delay difference T is calculated with the clock signal of the near-end clock source A The delay time difference T A Transmitting to the far end through an optical fiber link;
time delay difference T A A clock difference of time between sending the pulse per second signal by the near end and receiving the pulse per second signal sent by the far end; the calculation formula is as follows:
T A ＝ΔT+T BA +t B +r A
Δ T is the delay difference T A And delay difference T B The clock difference therebetween; t is BA The optical fiber transmission time delay from the far end to the near end; t is t B Is the transmission delay of the remote B, r A Is the receive delay of the near end a;
meanwhile, a second pulse signal and a clock signal generated by a near-end clock source are provided for a phase modulator, and the phase modulator performs phase modulation on light output by a near-end laser according to the received electric signal output by a near-end balanced homodyne detector, converts the light into an optical signal S and outputs the optical signal S to a far end B through an optical fiber link;
a second pulse signal and a clock signal generated by a clock source at a far end B are provided for a phase modulator, and the phase modulator performs phase modulation on light output by a far end laser according to a received electric signal output by a far end balance homodyne detector to convert the light into a light signal P;
the far-end balance homodyne detector performs coherent demodulation on the received optical signal S and the output light of the far-end laser to obtain a modulation second pulse on the signal S; the obtained pulse per second signal is input into a far-end time measuring module and is compared with a clock signal of a far-end clock source to calculate a time delay difference T B ；
T B A clock difference of time between sending the pulse per second signal by the far end and receiving the pulse per second signal sent by the near end; the calculation formula is as follows:
T B ＝-ΔT+T AB +t A +r B
T AB for near-end to far-end fibre-optic transmission delay, t A Is the transmission delay of the near end A, r B Is the reception delay of the remote B;
according to the time delay difference T at the same time A And calculating the clock difference delta T to adjust the clock signal of the far-end clock source, thereby compensating delta T for the far-end clock source to realize time synchronization of the far end and the near end.
5. The phase modulated bi-directional time synchronization system of claim 3, wherein the clock difference Δ T:
in (1), since the same optical fiber link, T, is used to and fro the system AB -T BA =0; and t is A +r B -t B -r A Because the same modulation and demodulation modes are used at the far end and the near end and the item is a fixed value, the generated time difference is ignored by setting compensation before the system runs;
the clock difference Δ T is thus reduced to:
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